Heated Oxygen Sensor: Echo

A heated oxygen sensor is mounted on exhaust pipe in front of catalytic converter. This heated oxygen sensor is referred to as bank No. 1 sensor No. 1, or front oxygen sensor. Another heated oxygen sensor is mounted on exhaust pipe behind catalytic converter. This heated oxygen sensor is referred to as bank No. 1 sensor No. 2, or rear oxygen sensor.
To test heater resistance on heated oxygen sensor, disconnect electrical connector for appropriate heated oxygen sensor. Electrical connector for bank No. 1 sensor No. 1 is a Gray 4-pin electrical connector located near exhaust pipe. See Fig 1. Electrical connector for bank No. 1 sensor No. 2 is a Gray 4-pin electrical connector located below passenger's side front seat and carpet, near center console. See Fig 2.
Using ohmmeter, check resistance between +B and HT terminals on electrical connector. See Fig 1 and Fig 2 . Replace heated oxygen sensor if resistance is not 11-16 ohms at 68°F (20°C). See HEATED OXYGEN SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL & INSTALLATION - 4-CYLINDER article.
If problem exists with either heated oxygen sensor, heater or wiring circuit, a Diagnostic Trouble Code (DTC) may be stored in Engine Control Module (ECM). See TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article for retrieving of DTCs.

Fig 1: Locating Electrical Connector & Testing Heated Oxygen Sensor Bank No. 1 Sensor No. 1 (ECHO)

Fig 2: Locating Electrical Connector & Testing Heated Oxygen Sensor Bank No. 1 Sensor No. 2 (ECHO)